The invention relates to a device for cooling sheets of glass by jets of air emitted by nozzles.
The rapidity with which glass is cooled affects its mechanical properties and, in particular, its behavior relative to impacts and its surface hardness. It is possible to allow the glass to cool slowly, generally in a float glass lehr. In this case, the final glass is able to be cut but when it fractures it is transformed into large pieces with sharp edges which is sometimes regarded as unsatisfactory in terms of safety. To provide the glass with improved shock-proof properties (fracture into small blunt pieces) it is possible to semi-harden, harden or temper the glass, which may be obtained by more rapid cooling. This accelerated cooling of the glass is generally implemented by blowing cold air onto the hot glass via nozzles.
Numerous types of nozzles have already been disclosed. In particular, WO00/23387, WO99/12855, WO2006/076215, U.S. Pat. No. 3,881,907 teach nozzles in the form of pipes which are placed horizontally beneath the moving sheets and of which the length (horizontally) corresponds to the width of the sheets to be cooled. The nozzles are perforated with holes or comprise a slot for the ejection of air towards the glass. Thus the nozzle in this case is a horizontal pipe closed at one end and arranged transversely relative to the direction of movement of the glass.
U.S. Pat. No. 3,393,062 teaches nozzles in the form of tubes terminated by a cone, of which the section is increased in the direction of flow of the airflow. U.S. Pat. No. 2,948,990, U.S. Pat. No. 4,519,829 and U.S. Pat. No. 4,578,102 teach nozzles in the form of tubes terminated by a cone, of which the section is reduced in the direction of flow of the airflow.
U.S. Pat. No. 5,562,750 teaches conical nozzles of which the section is increased in the direction of flow of the airflow, the nozzle being terminated by a grille.